RU2781466C1 - Fatigue test unit for samples - Google Patents

Abstract

FIELD: testing.

SUBSTANCE: invention relates to testing equipment, namely, to units for fatigue testing of materials. Unit comprises a frame for securing the test sample and an electromagnetic exciter; a power supply and automation unit; and means for measuring the parameters of the oscillatory process and monitoring the oscillation mode. The unit is additionally equipped with a vibration acceleration sensor connected with the power supply and automation unit connected, in turn, to the coil of the electromagnetic exciter made on a U-shaped coiled tape core; wherein one end of the core is rigidly secured in the frame, located thereon is a coil connected with the power supply and automation unit, and the other end of the core is cut in a yoke shape, configured to be attached to the sample, and acts as an armature.

EFFECT: increase in the accuracy of estimating the elastic component of the properties of the tested sample materials in fatigue testing.

1 cl, 4 dwg

Description

The invention relates to testing equipment, namely to installations for testing the fatigue of materials.

Known methods for testing samples of materials are most fully described in fundamental monographs [1].

The application of one method or another is determined by the purpose of studying the samples [2, 3].

A device for fatigue testing [4] is known. The device contains a clamp, the device for fastening the clamp is provided with a resonant element fixed on the body of the device, with a load mounted on it with the possibility of movement. The clamp elements are made in the form of a single-tooth grip and two profile lodgements located opposite to each other. In this device, in-phase oscillations of the test sample are implemented with a resonant oscillation located coaxially with the tested part.

A disadvantage of the known device is the dynamic measurement errors of the bending moment acting in the root part of the test sample, depending on the frequency of loading.

Closest to the proposed invention is a facility for fatigue testing [2, p. 183], chosen as a prototype.

The installation is equipped with electromagnetic excitation of oscillations. In the clamp on a massive frame, a beam with a load at the free end is reinforced. A gripper for clamping the test sample and an armature of the electromagnetic exciter are mounted in the cargo. By changing the overhang of the beam and the mass of the load, it is possible to set the required oscillation frequency of this system.

The disadvantages of such an installation are the difficulty of balancing the amplitudes in a self-oscillating system and the implementation of only a symmetrical loading cycle.

The technical problem solved by the invention is the creation of a facility for testing materials for fatigue, which provides tests for cantilever bending in one plane according to a "soft" loading scheme.

Soft loading - the excitation of dynamic loads, in which the given value is a load that is practically constant throughout the test. In this case, the displacement is not limited kinematically and may vary depending on the change in the stiffness of the loaded system during the period of growing fatigue damage and the gradual development of a fatigue crack.

The technical result from the use of the invention is to increase the accuracy of assessing the elastic component of the properties of the studied materials of the samples during fatigue tests.

The specified technical result is achieved by the fact that the installation for testing materials for fatigue, containing a frame for mounting the test sample and an electromagnetic exciter, a power supply and automation, means for measuring the parameters of the oscillatory process and monitoring the shape of vibrations, is equipped with a vibration accelerating sensor connected to the power supply and automation , which in turn is connected to the coil of an electromagnetic exciter made on a U-shaped twisted tape core, while one end of the core is rigidly fixed in the frame, and a coil is located on it, connected to the power supply and automation, and the other end of the core is cut off under the yoke , with the possibility of attachment to the sample and serves as an anchor.

The installation provides the following measuring instruments: frequency measurement; counting the number of loading cycles; measurement of oscillation amplitude by optical method; measurement of oscillation amplitude by photoelectric method; measurement of vibration amplitude by the method using a piezoelectric vibration acceleration sensor; measurement of the average value of the current in the exciter coil; observation of the oscillatory process using an oscilloscope.

The invention is illustrated by the following figures, which show:

Fig. 1 - constructive scheme of the installation;

Fig. 2 is a plot of the change in current over time;

Fig. 3 is a graph of the dependence of the electromagnetic force and the elastic force over time;

Fig. 4 is a graph of the sample displacement depending on the current flow and its interruption from time to time during the operation of the installation.

The installation contains three main parts located separately: a frame 1 designed for fastening a test sample 2 and an electromagnetic exciter 3; power supply and automation unit 4, designed to power the coil 5 of the electromagnetic exciter 3 with a current of the required magnitude and frequency; means for measuring the parameters of the oscillatory process and monitoring the form of vibrations 6.

Bed 1 is a massive L-shaped metal block, which is installed on the table through vibration isolators. Sample 2 is rigidly fixed at one end to frame 1. At the other end of sample 2, ferromagnetic armature 7 of electromagnetic exciter 3 is fixed. registering the oscillations of the sample 2), which is connected to the power supply and automation 4, which in turn is connected to the coil 5 of the electromagnetic exciter 3. The electromagnetic exciter 3 is made on a U-shaped twisted tape core 11. One end of this core is rigidly fixed in the frame 1, serves as stator 8 and coil 5 is located on it. The other end of the core is cut off under the yoke, attached to sample 2 and serves as anchor 7. The installation works as follows:

The frame 1 perceives the oscillations of the sample 2 and transmits them to the piezoelectric vibration acceleration sensor 10. The signal from the sensor 10 enters the power supply and automation unit 4, which in turn feeds the coil 5 of the electromagnetic exciter 3. To prevent the superposition of vibrational energy waves and improve the accuracy of their transmission, the frame 1 and the coil 5 assembled together with the stator 8 of one end of the core 11 of the electromagnetic exciter 3 are separated by vibration isolators in the form of vibration isolation pads 9.

The coil 5 of the electromagnetic exciter 3 is powered by a pulsating current from the power supply (Fig. 2).

When the current flows, an electromagnetic force arises, under the influence of which the armature 7 with the sample 2 moves down (Fig. 3). When the current is interrupted, sample 2 tends to return to its original position under the action of the elastic force (Fig. 3) (Fig. 4). Thus, cyclic loading is carried out in the presented installation, and the full cycle of movement of the loaded end of the sample during operation is demonstrated (Fig. 4).

The control of the parameters of the oscillatory process under cyclic loading of the sample and the observation of the form of vibrations are carried out using measuring instruments 6.

Based on the results of repeatedly repeated cycles, the parameters of high-cycle fatigue and amplitude-frequency characteristics are determined to assess the frequency properties, which depend on the role of the elastic component of the material under study under cyclic loading, and also determine the endurance limit.

Thus, the loading-unloading cycle of the sample is carried out during testing according to the “soft” scheme of flat cantilever bending implemented by this installation.

The proposed facility for testing materials for fatigue can be made, for example, from manufactured or finished parts. For example, electromagnetic exciter 3 is made of a U-shaped twisted tape core GOST 22050-76 using copper wire PEV with a diameter of 1.2 mm GOST 7262-78; vibration isolators type DO-38; vibration isolation pads VEP TU 22.19.20-002-04941811-2017; piezoelectric vibration acceleration sensor 10 type PAMT-16K.

The bed 1 is made of cast iron, in order to ensure high rigidity of the installation. The coil 5 of the exciter 3 is wound with a PEV wire with a diameter of 1.2 mm GOST 7262-78, divided into two halves of 90 turns each, located on different rods of the U-shaped core. The coils are connected in series and matched.

Piezoelectric vibration acceleration sensor 10 of the PAMT-16K type is glued to the frame 1 at some distance from the exciter stator 8. Power supply unit of the NLS-3024 type. As measuring instruments 6 can be used: a universal pulse counter Aries SI8 for counting cycles and loading frequencies (Fig. 3); a digital voltmeter of type B7-17 and an oscilloscope of group C1 for monitoring the oscillatory process and recording the magnitude and shape of the signal of the piezoelectric sensor (Fig. 2); multimeter Aries IMS-F1 for measuring current; to measure the oscillation amplitude (Fig. 4) by optical, photoelectric and indirect methods, the following are used: non-contact inductive sensor KIPPRIBOR, series LA; non-contact optical sensors VBZ; vibration velocity sensor with current output type DVST.

Thus, the proposed facility for testing materials for fatigue in comparison with the prototype makes it possible to improve the accuracy of estimating the elastic component of the properties of the studied materials of the samples during fatigue tests due to the fact that during the testing process, the unloading of the sample occurs due to elastic forces, and loading by the electromagnetic unit. High accuracy is achieved due to the coordinated distribution of the electromagnetic force and the elastic force and the corresponding displacement of the sample depending on the current flow and its interruption in time during the operation of the installation. In general, the facility for testing samples for fatigue is simple in design - it uses standard tested parts and assemblies, is technologically advanced and easy to use.

Literature.

1. Shkolnik L.M. Fatigue testing technique. Directory. M.: Metallurgy, 1978. - 304 p.

2. Test equipment: Handbook. In 2 books. / Ed. V.V. Klyuev. - M.: Mashinostroenie. 1982. Book. 1.-528 p.

3. Methods of mechanical testing of metals. Fatigue test methods GOST 25.502-79.

4. Copyright certificate SU 1838773 A3 G01N 3/04, 08/30/1993.

Claims (1)

Installation for testing samples for fatigue, containing a frame for mounting the test sample and an electromagnetic exciter, a power supply and automation, means for measuring the parameters of the oscillatory process and monitoring the shape of vibrations, characterized in that it is equipped with a vibration acceleration sensor connected to the power supply and automation, which in turn, it is connected to the coil of an electromagnetic exciter made on a U-shaped twisted tape core, while one end of the core is rigidly fixed in the frame, and there is a coil connected to the power supply and automation unit on it, and the other end of the core is cut under the yoke with the possibility attachment to the sample and serves as an anchor.

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